Method of making an elongated singly coiled filament and mounting it in a tubular incandescent lamp

ABSTRACT

The elongated filament of a lumiline- or showcase-type incandescent lamp is initially wound as a coiled coil filament and attached to the lead wires of the mount assembly. When a getter is used, the getter is applied to the primary turns of the coiled coil filament before it is stretched and remains on the primary turns of the resulting singly coiled filament that is attached to the mount assembly.

United States Patent Inventor Erik N; Giertsen Verona, NJ.

Appl. No. 18,227

Filed Mar. 10, 1970 Patented Dec. 28, 1971 Assignee WestinghouseElectric Corporation Pittsburgh, Pa.

METHOD OF MAKING AN ELONGATED SINGLY COILED FILAMENT AND MOUNTING IT INA TUBULAR INCANDESCENT LAMP 6 Claims, 3 Drawing Figs.

U.S. Cl. 29/25.!5, l40/7l.5, l40/71.6 Int. Cl 1-101] 9/18, H01] 9/36Field 01 Search 140/7 I .6, 71.5", 29/251, 25.11, 25.13, 25.17, 25.18,25.14, 25.15

References Cited UNITED STATES PATENTS Zabel Spaeth.... Cartun CurtisWeiss Armstrong Berlec Primary Examiner.lohn F. Campbell AssistantExaminer-Richard Bernard Lazarus AttorneysA. T. Stratton, W. D. Palmerand D. S. Buleza 29/2518 X 29/2514 X 313/285 X 29/2518 X 117/219 XABSTRACT: The elongated filament of a lumilineor showcase-typeincandescent lamp is initially wound as a coiled coil filament andattached to the lead wires of the mount assembly. When a getter is used,the getter is applied to the primary turns of the coiled coil filamentbefore it is stretched and remains on the primary turns of the resultingsingly coiled filament that is attached to the mount assembly.

METHOD OF MAKING AN ELONGATED SINGLY COILED FILAMENT AND MOUNTING IT INA TUBULAR INCANDESCENT LAMP BACKGROUND OF THE INVENTION 1. Field of theInvention The present invention relates to electric lamps and hasparticular reference to an improved method of making elongated singlycoiled filaments and mounting them on the lead wires of tubularincandescent lamps of the lumiline or showcase type.

2. Description of the Prior Art So-called lumilineand showcase-typeincandescent lamps are well known in the art and contain an elongatedsingly coiled filament of suitable refractory metal wire, such astungsten, that is electrically connected to the lead wires of a supportassembly which holds the filament in suspended position within a tubularenvelope. Showcase lamps are of the singleended type and have a threadedbase at one end that permits the lamp to be used in conventionalthreaded socket fixtures. A showcase lamp of this type is disclosed inUS. Pat. No. 2,425,865 issued Aug. 19, 1947 to R0. Cartun. So-calledlumiline" lamps, on the other hand, are double ended and the elongatedfilament is electrically connected to a metal cap that is sealed to eachend of the glass envelope. A lumiline lamp constructed in this fashionis disclosed in US. Pat. No. 2,667,594 issued Jan. 26, 1954 to H.E.Hermanson et al.

Heretofore, the filaments for such lamps were wound as singly coiledhelices that were stretched to the required length and clamped to thelead wires. In order to obtain a stretched filament of the requiredelectrical characteristics, it was necessary to wind the fine tungstenwire on very large mandrels. In the case of a conventional 60-watt T8lumiline lamp for example, the diameter of the mandrel is over 13 timesas large as the diameter of the tungsten wire. The percent mandrel isaccordingly over 1,300 percent which makes it very difficult tomanufacture such filaments.

In addition, due to the dimensions of lumilineand showcase-type lampsthe prior art singly coiled filaments as wound were inherently long anddifficult to handle. In the case of the aforementioned 60-watt T8lumiline lamp for example, the finished coil length (prior tostretching) is approximately 27 millimeters. The finished coils have anuncoiled leg at each end and accordingly have a tendency to tangle andbecome locked with one another when handled and shipped en masse.Shrinkage is accordingly high and gettering a batch of such coilsrequires extreme care to insure that the coils are properly coated withgetter and do not become entangled. The singly coiled filaments used inthe prior art are accordingly difficult and inefficient to manufactureand ship and present serious shrinkage and quality control problemsduring the gettering and filament-mounting operations.

SUMMARY OF THE INVENTION The foregoing problems and disadvantagesassociated with the prior art singly coiled filaments used inlumilineand showcase-type incandescent lamps are avoided in accordancewith this invention by initially winding the filament as a coiled coilhelix and then stretching it into a singly coiled helix of the properlength that is attached to the lead wires of the support assembly. Dueto their coiled coil configuration, the filaments as wound are muchshorter and easier to handle and getter in bulk quantities since they nolonger have a tendency to tangle. The relative size of the primarymandrel on which the fine tungsten wire is wound is also greatlyreduced, thus facilitating the coil-winding operation and reducing themanufacturing cost of the filaments. Since the coiled coil filamentsinherently have a larger diameter and are shorter than the conventionalsingly coiled filaments, they can be shipped en masse and then bereadily segregated, stretched and attached to the lead wires by factorypersonnel.

BRIEF DESCRIPTION OF THE DRAWINGS A better understanding of theinvention will be obtained by referring to the exemplary embodimentshown in the accompanying drawings, wherein:

FIG. 1 is an elevational view, partly in section, ofa lumiline lamp thatcontains the improved coiled filament of the present invention;

FIG. 2 is an enlarged fragmentary view of the embryonic filamentillustrating the manner in which the refractory metal wire is woundaround the primary mandrel to form a composite wire which issubsequently wound into coiled coil configuration; and,

FIG. 3 is an enlarged fragmentary view of the finished coiled coilfilament after the primary and secondary mandrels have been removed andbefore it is stretched to its final length and mounted.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1 there is shown arepresentative lumiline incandescent lamp 10 which embodies the presentinvention and consists of a sealed tubular glass envelope 12 that hasmetal caps 13 and I4 fused to each end and contains an elongated singlycoiled filament 16 of suitable refractory metal wire such as tungsten.The filament 16 is coaxially suspended within the envelope 12 bystublike conductor members such as lead wires 18 and 20 that are clampedaround the ends of the filament and secured, as by spot welding, to apair of terminal leads 22 and 24 that are fastened to an elongated rigidsupport assembly 25 that extends along the wall of the envelope 12. Thesupport assembly 25 comprises a metal channel 26 that is spot welded tothe terminal lead 22 and has its opposite end embedded in a glassinsulator 27 that is fused and anchored to the end of the other terminallead 24. The terminal leads 22 and 24 are compressively seated againstand thus are in electrical contact with the respective caps 13 and 14which serve as the lamp terminals. The support assembly 25 is preventedfrom moving laterally by a U-shaped wire harness 30 that is spot weldedto the channel 26 and resiliently engages the curved walls of theenvelope l2.

Sagging of the elongated filament 16 is prevented by a series ofintermediate support wires 28 that are loosely looped around thefilament l6 and have their opposite ends embedded in glass beads 29 thatare fused and anchored to the metal channel 26. One end of the envelope12 is provided with a glass tubulation (not shown) which is tipped offin the usual manner after the envelope 12 has been evacuated. The lamp10 is of the vacuum type and the filament 16 is coated with a suitablegetter material which is vaporized during the lampflashing operation andpurges the sealed envelope 12 of residual gaseous impurities in thewell-known manner.

In accordance with the present invention, the filament 16 is initiallyformed as a coiled coil instead of a singly coiled helix. As shown inFIG. 2, this is accomplished by winding the tungsten wire around aprimary mandrel 19 of the dissimilar metal such as molybdenum to form acomposite wire 16 of predetermined length X that consists of the primarymandrel I9 and a plurality of uniformly spaced primary turns 17 of finetungsten wire. This composite wire 16' is then wound on a largersecondary mandrel (not shown) to provide an embryonic coiled coil helixof predetermined diameter and length. The secondary coiling operation isperformed on a coiling machine which mechanically withdraws thesecondary mandrel from the coiled coil after it has been formed. Suchcoiling machines are well known in the art.

After the second coiling operation has been completed, the primarymolybdenum mandrel 19 is removed by immersing the embryonic coiled coilsin a bath of sulfuric and nitric acids which dissolves and removes themolybdenum mandrel but does not dissolve the tungsten wire. The finishedcoiled coil filament 32 is shown in FIG. 3 and consists of a compoundhelix of predetermined-length Y and diameter Z which has a predeterminednumber of spaced secondary turns 34, a

predetermined number of spaced primary turns 17, and longitudinallyextending singly coiled legs 35 at each end.

The finished coiled coil filaments 32 are spray coated with a suitablegetter material and dried in masse by placing them in an oven in thecustomary manner.

Mounting of the gettered coiled coil filaments 32 is accomplished byclamping the end of one of the coil legs 35 within the hooked end of oneof the stub leads 18, 20 of the support assembly 25 and pulling theother coil leg 35 to stretch and convert the coiled coil into a singlycoiled filament 16 of the type shown in FIG. 1 that is slightly longerthan the spacing between the stub leads l8 and 20. The free end of thestretched singly coiled filament 16 is then slipped through the loops ofthe support wires 28 and clamped to the hooked end of the other stublead, thus completing the assembly of the filament mount. The length Xof the primary coil and length Y of the coiled coil 32 are such that thelatter is stretched to a length at mounting that is greater thandimension X. Hence, the coiled coil helix 32 is stretched into a singlycoiled helix which, in turn, is stretched into a singly coiled filament16 of the proper length.

Surprisingly, it has been found that very little, if any, of the coatedgetter material is dislodged from the primary coil turns 17 when thecoiled coil filament 32 is stretched. Due to the manner in which thefilament 16 is manufactured and then mounted on the stub leads 18 and20, the segment of the filament leg 35 is located within and extendsbeyond one of the lead wire clamps consists of primary turns 17 that arespaced closer together than the primary turns in the main. body portionof the stretched filament 16. In a conventional lamp, the coil legsusually comprise uncoiled segments of wire and these are clamped withinthe lead wire hooks.

While the invention has been illustrated and described in terms of alumuline lamp, it can be employed with the same manufacturing and costreduction advantages in other types of lamps, such as showcase lamps,which require long singly coiled filaments of small diameter, or even inlamps which utilize uncoiled filaments.

SPECIFIC EXAMPLE As a specific example, excellent results have beenobtained in the case of a 60-watt T8 lumiline lamp of the type shown inthe drawing by winding a tungsten wire 0.05 millimeter in diameteraround a primary molybdenum mandrel having a diameter of 0.117millimeter to form a composite wire 91.6 millimeters long (dimension X)and 0.217 millimeter in diameter with a primary winding of 340 turns perinch. The percent mandrel (diameter of mandrel divided by diameter ofwire) was accordingly 234 percent. The composite wire was wound on aretractable secondary mandrel 0.401 millimeter in diameter (185 percentsecondary mandrel) at 79 t.p.i. to provide a coiled coil that had alength of 19.1 millimeters (dimension Y), a barrel diameter of 0.835millimeter (dimension Z), and contained 44 secondary turns. The primaryturns of the finished coiled coil filament were spray coated with agetter consisting of 77 percent by weight cryolite and 23 percent byweight red phosphorus suspended in a suitable liquid vehicle such amixture of nitrocellulose and amyl acetate, which serve as a binder anda thinner, respectively. The spacing between he stub leads of the lampmount was 436 millimeters and the gettered coils were stretched to aslightly longer length at mounting.

in contrast, the filament heretofore used in the same type lumiline lampconsisted of a singly coiled filament that was formed by winding aODS-millimeter diameter tungsten wire around a primary mandrel 0.66millimeter in diameter (1,320 percent mandrel) at 316 t.p.i. Theresulting singly coiled filament was 26.7 millimeters long, 0.76millimeter in diameter and was stretched to a length slightly in excessof 436 millimeters prior to mounting. Tests have shown that theshrinkage during coil winding was frequently over 20 percent in the caseof the prior art singly coiled filaments and that less than 1 ercent srlnkage occurred when the filaments were initially wound as coiled coilsand subsequently stretched in accordance with the invention.

It will be apparent from the foregoing that an improved method has beenprovided for manufacturing elongated filaments for electric lamps andmounting them on the support assembly which reduces the cost of thefilament and lamps. The invention permits the filaments to be wound inan efficient manner and then be handled and shipped in bulk quantitieswithout becoming tangled or distorted.

I claim:

1. In the manufacture of an electric incandescent lamp having anelongated singly coiled filament of refractory metal wire that is heldin suspended position within a tubular envelope by a support structurethat includes a pair of spaced conductor members, the method of makingsaid filament and mounting it on said support structure, which methodcomprises;

initially winding the refractory metal wire into a coiled coil filamentthat is shorter than the spacing between said conductor members,stretching and thereby converting said coiled coil filament into asingly coiled filament having a plurality of spaced primary turns and alength that is slightly longer than the spacing between said conductormembers, and then attaching the ends of said stretched singly coiledfilament to the respective conductor members so that said filament issuspended therebetween.

2. The method of claim I wherein;

said conductor members comprise a pair of lead wires and said stretchedsingly coiled filament is attached to said lead wires by forming thefree ends of the wires into hooks and closing said hooks around the endsof the filament.

3. The method of claim I wherein;

the primary turns of said coiled coil filament are coated with gettermaterial before the coiled coil filament is stretched into a singlycoiled filament, and

the length of said coiled coil filament and the initial spacing betweenthe primary turns thereof are such that the coated getter materialremains on the primary turns of the stretched singly coiled filament.

4. The method of claim 1 wherein;

said coiled coil filament is formed by winding the refractory metal wireon a primary mandrel to provide a composite wire,

said composite wire is wound on a secondary and larger mandrel to forman embryonic coiled coil filament having a longitudinally extendingsingly coiled leg at each end, and

said primary and secondary mandrels are removed from the embryoniccoiled coil filament to provide a finished coiled coil filament.

5. The method of claim 4 wherein;

said refractory metal wire comprises tungsten wire,

said primary mandrel is composed of molybdenum and is chemicallydissolved from the embryonic coiled coil filament and said secondarymandrel is mechanically withdrawn from the embryonic coiled coilfilament.

6. The method of claim 4 wherein the length of said finished coiled coilfilament compared to the spacing between said pair of conductor membersis such that both the coiled coil filament and the resulting singlycoiled filament are stretched before the latter is attached to saidconductor members.

t t i

1. In the manufacture of an electric incandescent lamp having anelongated singly coiled filament of refractory metal wire that is heldin suspended position within a tubular envelope by a support structurethat includes a pair of spaced conductor members, the method of makingsaid filament and mounting it on said support structure, which methodcomprises; initially winding the refractory metal wire into a coiledcoil filament that is shorter than the spacing between said conductormembers, stretching and thereby converting said coiled coil filamentinto a singly coiled filament having a plurality of spaced primary turnsand a length that is slightly longer than the spacing between saidconductor members, and then attaching the ends of said stretched singlycoiled filament to the respective conductor members so that saidfilament is suspended therebetween.
 2. The method of claim 1 wherein;said conductor members comprise a pair of lead wires and said stretchedsingly coiled filament is attached to said lead wires by forming thefree ends of the wires into hooks and closing said hooks around the endsof the filament.
 3. The method of claim 1 wherein; the primary turns ofsaid coiled coil filament are coated with getter material before thecoiled coil filament is stretched into a singly coiled filament, and thelength of said coiled coil filament and the initial spacing between theprimary turns thereof are such that the coated getter material remainson the primary turns of the stretched singly coiled filament.
 4. Themethod of claim 1 wherein; said coiled coil filament is formed bywinding the refractory metal wire on a primary mandrel to provide acomposite wire, said composite wire is wound on a secondary and largermandrel to form an embryonic coiled coil filament having alongitudinally extending singly coiled leg at each end, and said primaryand secondary mandrels are removed from the embryonic coiled coilfilament to provide a finished coiled coil filament.
 5. The method ofclaim 4 wherein; said refractory metal wire comprises tungsten wire,said primary mandrel is composed of molybdenum and is chemicallydissolved from the embryonic coiled coil filament and said secondarymandrel is mechanically withdrawn from the embryonic coiled coilfilament.
 6. The method of claim 4 wherein the length of said finishedcoiled coil filament compared to the spacing between said pair ofconductor members is such that both the coiled coil filament and theresulting singly coiled filament are stretched before the latter isattached to said conductor members.